In a thermography arrangement, such as an IR camera, various environmental factors and other sources may influence or otherwise affect previously calibrated measurement accuracy of the thermography arrangement. For example, an original calibration of an IR camera or module may no longer be suitable (e.g., no longer producing accurate radiometric measurements) due to heat from nearby electronic components or other sources within a case that houses an IR camera or module. In another example, an original calibration may not be suitable for some thermal environments to which the IR camera or module may be subjected in field use (e.g., thermographic applications outside in a cold winter weather). Also, various characteristics of various components of the IR camera or module may change with passage of time and/or with use, which may lead to calibration drifts (e.g., temperature drifts) and/or non-uniformities in captured infrared images.
To correct for such non-uniformities and temperature drifts in conventional systems, a mechanically operated calibration shutter mounted immediately in front of infrared detectors is raised into position in front of the detectors to block off all incoming energy from a real world scene, and allow the detector to be calibrated against a fixed smooth source with a uniform known temperature. This calibration is required at intervals varying from a few seconds to a few minutes, depending on the factors that cause detector drift at any time.
In one conventional method for calibrating an infrared imaging system, a mechanical shutter is initially used. The infrared imaging system thereafter relies on an imager algorithm that functions with a calibration curve created for the imaging system, with the curve comprising a plot of system output versus target scene temperature. An initial base output is obtained with a closed shutter that is later used in conjunction with the calibration curve and real-time measurements from the imaging system, and the base output serves as a reference measurement in calculating the output of the detector elements attributable to the target scene on an ongoing basis without necessitating further actuation of the shutter.
However, the need for reduction of unnecessary moving parts, reducing system weight and power consumption has led to the development of thermography arrangements without a shutter (also referred to as “shutterless” arrangements) where the mechanical shutter is removed. The removal of the mechanical shutter requires new methods of calibration to address calibration issues related to IR radiation detection, such as temperature drifts of the detector and non-uniformities of the detector. For example, in a shutterless camera the initial reference measurement cannot be obtained as there is no known reference, such as a shutter, to obtain this initial reading from. In addition, conventional methods involving a calibration curve projecting non-uniformities and temperature drifts based, for example, on ambient temperature obtained typically in a controlled environment such as a laboratory, is not valid for all environments and types of uses that thermography arrangement might be subjected to.
Therefore, there exists a need for facilitating or enabling improved calibration of captured infrared data values by an IR imaging system in a shutterless thermography arrangement.